Telephone exchange system



July 2, 1935. w, w, (:ARPENTER 2,006,438

TELEPHONE EXCHANGE SYSTEM Filed 0ct .20, 1954 z'sheets-sheet' 2 #msr oscoozn //v TERMED/ATE' mzcoam LAST .DECODER v I INVENTOR.

WWCARPENTER ATTORNEY trunkedfrom the originating office.

Patented July 2, 1935 ilNi'lED STATES PA'iNT oFFice- 2,006,438 TELEPHONE EXCHANGE SYSTEM Warren W. Carpenter, Garden City, N. Y., as-

signor to Bell Telephone Laboratories, Incorporated, New York New York, N. Y., a corporation of Application October 20, 1934, Serial No. 749,250

Claims. (Cl. 179-18) In exchange areas having a large number of local ofiices it is not economical to provide direct groups of trunks for interconnecting any two offices of the exchange, particularly where the traffic between certain widely separated ofiices is very heavy. In some exchange areas, there fore, it is more economical to route trafiic between certain ofiices through a tandem office which serves as a common intermediate distributing point.

' It is an object of this invention to render more efficient the comparatively smaller number of trunks in a group directly interconnecting any two offices by reducing the number of the direct trunks to the maximum required for handing normatically rerouting the abnormal or overflow traiiic between such oflices to a tandem ofiice where it is directly routed to the desired ofiicel In systems of the type disclosed in Patent No. 1,862,549, granted June 14, 1932, to R. Raymond and W. J. Scully, the establishment of connections -from an originating office to any other oflice of the exchange area is made possible by district and oflice selectors which are set to selectan idle trunk of the group of trunks extending to the oflice in which a desired subscribers line terminates, by a sender common to all calling subscribers lines of the originating office. A plurality of senders, any of which may be taken for use by a calling line, is provided, each sender having registers for registering both the oflice and numerical designations or" a desired line dialed by a calling subscriber and contr'olling apparatus for controlling the setting of adistrict and an oflice selector to extend a connection to the oifice in which'the desired line terminates and for controlling other appartus in the selected office for completing the connection. A plurality of decoders is also providedcommon to all of the senders, an idle one of which becomes associated with a sender taken for use by a calling subscriber. The decoder is provided with ofiice code registers to which the ofiioe code is transferred from the registers of the associated sender and is also provided with as many route relays as there are trunking points to which calls may be The combined setting of the-ofiice code registers of the switches group to thetandem office. I

operated are locked and the .chain operating cirdecoder determines which one of these routerelays shall be operated for any particular call. The operated route relay is then instrumental in establishing in the associated sender a registration of the class of the call-and a decoded office'code 5 registration for directing the sender to control the setting of the district and ofiice selector switches or the setting of the district selector alone toselect a group of trunks extending to the offioe-in which the desired line terminates. 10

In accordance with the present invention, if at the time the decoder is taken for use by a sender, all trunks of any interoffice group of trunks are atthe time busy, indicating that it would not at that time be possible to complete a connection over that trunk group, a chain circuit is established through contacts of operated relays of the trunks of that trunk group which operates a reroute relay in the decoder. When, therefore, an ofiice code registration is set up in the decoder which would normally cause the mal trafiic between the two offices and byauto operation of a direct route relay for routing a connection to that particular trunkgroup', with the reroute relay of that particular trunk group operated, the circuit for operating the direct route relay is .transierredto the winding of a tandemroute relay which will cause the rerouting' of the connection over another trunk group extending to a tandem ofiice. With the tandem route relay operated, the sender is then caused, in the manner described in the patent to Raymond and Scully, above referred to, to establish a connection to the indicated tandem ofiice from which office the connection is further extended to the desired oi'fice. Since the rerouting takes place in the decoder prior to the settingup of the decodedioffice code registration in the sender and the starting of the sender to control selector in accordance therewith, selector 4 switches are not set by the sender to attempt the establishment of a connection to a trunk of the desired busy trunk group, but are set to establish the connection over the alternate trunk The decoder is provided with as many reroute relays as there are interofiic'etrunk groups over which connections may be established and at any time as many of these reroute relays will sender all reroute relays which are at the time cuits of all reroute relays are opened until after the decoder has been dismissed.

For a clearer understanding of the invention reference may be had to the following detailed description read in connection with the accompanying drawings of which:

Fig. 1 shows schematically a calling subscribers line, a line finder, district selector, office selector, link circuit, sender and decoderconnector of an originating office; a subscribers line, incoming selectors and a final selector of a distant office, a group of direct trunks extending between the ofiices and a tandem ofiice indicated by a rectangle through which connections may also be established between the originating and distant ofiices;

Fig. 2 shows the last trunk of the direct trunk group together with the sleeve relays of all trunks of the group and a chain busy circuit controlled thereby;

, Fig. 2A shows a modification of a direct trunk; and

Fig. 3 shows such portions of one decoder, accessible from the decoder-connector of Fig. l, as are necessary to an understanding of the invention and other decoders schematically illustrated by the dot-dash rectangles also accessible from the decoder-connector.

The line finder Edi, district selector N32, ofiice selector lill, district finder Hi3 and sender selector 04 of the link. circuit, sender Hi5 and decoder-connector E66, being of the well-known type and functioning in the usual manner, have for the sake of simplification been disclosed only schematically herein. For a complete disclosure and description thereof, reference may be had to Patent No. 1,862,549 granted to R. Raymond and W. J. Scully, hereinbefore referred. to. The decoder .300, only such portions of which as are deemed necessary to an understanding of the present invention have been disclosed, is of the type disclosed in the aforementioned patent. The tandem office equipment indicated by the rectangle Hill of Fig. l is of the type disclosed in detail in Patent No. 1,840,132 granted January 5, 1932, to H. Roberts. The incoming selectors I09 to 5 22, inclusive, and the final selector H3 are also of the well-known type and therefore have been only schematically indicated.

In order that the invention may be more clearly understood, it will be assumed that the sub scriber at substation Hill of an originating oifice of an exchange area desires to establish a connection with a subscribers line I M which terminates at a distant office oi the exchange area and, upon removing his receiver from the switchhook, obtains a. connection with an idle sender I05 in the originating ofiice through the operation of line finder iili, district finder I63 and sender selector 19A in the we1l-lnown manner and then dials the office code letters and numerical digits of the directorynumber of the wanted line H4.

In response to dialing, the office code and nu merical designations are registered in the sender in the well-known manner and followingv the registration of the letters of the oilice code designation the decoder-connector tilt is operated to associate an idle oneof a plurality of decoders with the sender. Three of the plurality of decoders are indicated by the rectangles 300, 30!

and 302 of Fig. 3. Assuming that the first decoder 300 is at the time free, the decoder-connector I06 causes the association thereof with the sender H35 and operates the decoder start relay 3l5.

Each decoder is provided with the usual receiving registers to which the associated sender transfers the registered office code designations, a route relay corresponding to each route over which connections may be extended from the originating office, and transmitting registers which are selectively set by any operated route'relay. The transmitting registers are employed to transfer routing information to registers of the ssociated sender which in turn control the function ing of the sender to establish the desired connection over district and orlice selectors or over a district selector only, by the route indicated by the operated route relay or" the decoder. Four of the route relays of decoder 389 are disclosed, of which relays 333 and 395 designate direct routes over which connections may be established from the originating office directly to different distant or terminating oi'hees and relays 3G4 and 396 designate tandem routes extending from the originating o ifice to different tandem oifices. If it be assumed that there are two hundred local terminating ofiices in the exchange area there would be two hundred direct route relays such as 393 and iii-5 and as many tandem route relays such as 39 and 3% as there are tandem ofiices in the area to which the originating oifice has access.

In addition to the usual equipment the decoder is also provided with a reroute relay corresponding to each direct route to which it is desirable to apply alternative routing. Two of the reroute relays Sill and 3&8 are disclosed. With the decoder the operating winding .of each reroute relay is normally connected to the all-trunks busy conductor of the group of direct inter-ofiice trunks forming a part of the corresponding direct route over the back contacts of a cut-off relay. Nine groups of such cut-off relays of four relays each may be provided, or thirty-six cut-off relays, over the back contacts of which the group busy conclusters of as many as two hundred direct groups of trunks may normally extend to the two hundred reroute relays if it should be required that alternative routing he applied to all direct routes. Two of these cut-oil relays are and 3m are disclosed. The nine groups of cut-off relays are in turn controlled by a smaller group of three relays (ii i, 352 and M3 which are in turn controlled by relay Sit .and decoder start relay 3E5. Thus, when the decoder is seized and the start relay 315 operates, relays 3M, 3! l, H2, 313 and all cutoff relays such as 309 and 3) become operated in cascade to disconnect the operating windings of all reroute relays of the decoder from the corresponding all-trunks busy conductors. An additional relay 315 is also provided which operates in parallel with relay 3M for providing locking grounds to the locking windings of all the reroute relays. The start relay 3l5 also functions in the usual manner to initiate the registration and translation functions of the decoder.

It will first be assumed that at the time decoder see is seized by the decoder-connector I36 the direct route extending to the office in which the wanted line H4 terminates is available and that only trunk I E5 of the group of trunks constituting this group is idle and that, therefore, there is no ground potential on the all-trunks busy conducto H6 individual to this group of trunks. Reroute relay 308 of the decoder allocated to the route of which the direct trunk group is a part will therefore be unoperated. When the decoder is seized and start relay 3 I operates, the decoder then proceeds to register the office code designations of the wanted line, transferred thereto from the office code registers of the sender, and to translate such office code by the operation of the proper direct route relay corresponding to the direct trunk group in which the idle trunk I !5 is located. This direct'route relay will be assumed to be relay ildBfland will-be operated in a circuit under the controlof the receiving registers of the decoder overthe' back, contact of reroute relay 308. With relayttlfioperated the transmitting registers of the decoder are selectively set and the proper routing information istransmitted to the sender the usual manner. As previously described, the. decoder start relay 3I5 also causes the operation of all cut-off relays, such as 308 and 31'0, thereby opening the operating circuits of all rerouterelays so that no reroute relay may be operated during the time that the decoder is'making a routing thereby preventing the mutilation of a routing that is at the time in progress.

The sender after receiving the required routing information thenproceeds to set the district selector Hi2 and the officeselector IU'I to extend the connection from the calling line to the proper trunk'group extending to the office of the wanted subscriber and, assuming that the trunk H5 of this group is the only idle trunk of the group, the ofilce selector makes connection therewith.

'The sender then controls the setting of the in coming selector III! in which this trunk terminates and the final selector I lit to complete the.

connection to the wanted line I I4.

- Following the transfer of routing information from the decoder 3% to the sender I05, the decoder is dismissed for use on another call and start relay 3I5 is released thereby in turn releasing all cut-off relays such as 309 and SID. Any reroute relay such as 3% may now be operated to change the routing on subsequent calls. The sender is also dismissed in the usual manner as soon as it has completed its functions.

Since it was assumed that at the time the previously clescribedcallwas initiated all but the last trunk H5 of the direct trunk group extending to the office of subscribers' line I It was busy, and since the previously established call has now busied this last trunk I IS, the chain circuit over the all-trunks busy conductor H6 is now established from ground over the serially connected contacts of the operated sleeve relays Ill-I l8 and H9 of all of the trunks of the group, conductor 3 I8, lower back contact of cut-oil relay 3 I i) of decoder 3%, to battery through the operating winding of reroute relay .308. Similar parallel circuits are established over back contacts of corresponding cut-off relays and to the corresponding reroute relays of all; other decoders such as 3M and 302. These reroute relays are thus operated indicating to all decoders that all trunksof the direct route extending from the originating office tothat particular distant office-are busy and that any subsequent calls to that office should be rerouted thereto through a tandem'oiiice.

If new another call to that particular ofiioe is initiated and for exampleythe decoder 300 is I seized, relay 3!! operates to start the functionoperated, a locking circuit is therefore closedthrough its locking Winding and lower contact to ground at a front contact of relay 3I6 before 386 or to the tandem oiiice I08.

the cut-off'relay 3H1 becomes'operated to open its initial operating circuit; With reroute relay 308 locked operated, the decoder proceeds to register the ofiice code information transferred thereto from the sender and to set the tandem route relay 306 in a circuit over the upper front contact of reroute relay 398 under the control of the receiving registers of the decoder. With a tandem route relay operated the transmitting registersof the decoder are selectively set and cause routing information to'be transmitted to the sender whereby the sender controls the setting of district selector I02 and oiiice selector It! to trunk the call over the tandem route corresponding to the operated tandem route relay known manner the sender I05 then transfers the required routing information to the tandem office sender which proceeds to further extend the connection to the distant ofiice and toset selector As disclosed in Fig. 2, each trunk of the group is provided with. a sleeverelay such as H9 which becomes operated assoon as the trunk is seized by an office selector or'by a district selector, the all-trunks busy conductor I I6 being grounded over the serially connected contacts of the sleeve relaysof all trunks of the-group as soon as all trunks of the grouphave been seized and made busy in. the establishment of connections. If, because of operating requirements, it is not desirable to employ a relay operated over the sleeve terminal of the trunk, the circuit arrangement disclosed in Fig. 2A may be employed. In ac-- cordance with the alternative arrangement, relay I28 operates over a trunk loop comprising the tip and ring conductors of thetrunk when the trunk is seized for use and upon operating, establishes anobvious operating circuit for relay IZI. Relay I2i upon operating locks to groundsupplied from In the wellthe office or district selector over the sleeve ter I minal of the trunk, shunts the winding or relay I20 and closes one pointin a chain circuit which may be extended to an all-trunks busy conductor suchas conductor H6.

From the preceding description of the invention, it will be apparent that all decoders of an originating ofiice are kept informed of the availability of all direct routes extending to other ofiices of the exchange area and that therefore prior to the functioning'of. a sender to establish a connection over any direct 'route to a desired office, the sender is given rerouting information whereby the connection may be routed indirectly to the desired o-ffice if there is no idle trunk available in the direct route. This obviates the necessity of breaking down a partially completed connection which can not be completed because of unavailable direct trunking facilities and the reestablishment of a new connection overan available indirect route thereby saving wear and holding time of equipment, current drain, and increasingfthe speed of establishment of connec-:

tions:

What is claimed is:

1. In a telephone exchange system, a calling o ifice, called offices, an intermediate oflice, switching mechanism located in said calling oflice, a

group of direct paths extending from said switch-- ing mechanism to each of said called offices, a group of indirect paths extending from said switching mechanism through said intermediate ofiice to each called ofiice', a register sender for recording the ofiice code designations of wanted lines and for controlling said switching mechanism to select a path to the called oiiice in which a wanted line terminates, a decoder associable with said sender having route relays corresponding to all groups of paths extending from said switching mechanism, operating circuits for said route relays controlled. from said sender in accordance with the office code'designation registered therein, and reroute relays in said decoder corresponding to all groups of paths extending from said switching mechanism, each of said reroute relays being operable when all paths of its corresponding group of paths are busy to transfer the circuit normally effective for operating the route relay corresponding to that group of paths to a route relay corresponding to said group of indirect paths.

.2. In a telephone exchange system, a calling ofiice, called offices, an intermediate oflice, switching mechanism located in said calling office, a group of direct paths extending from said switching mechanism to each of said called offices, a group of indirect paths extending from said switching mechanism through said intermediate Office to each called oflice, a register sender for recording the oflice code designations of wanted lines and for controlling said switching mechanism to select a path to the calling office in which a wanted line terminates, a decoder associable with said sender having route relays corresponding to all groups of paths extending from said switching mechanism, operating circuits for said route relays controlled from said sender in accordance with the office code designation registered therein, and reroute relays in said decoder corresponding to all groups of paths extending from said switching mechanism, each of said reroute relays being operable whenall paths of its corresponding group of paths are busy to transfer the circuit normally effective for operating the route relay corresponding to that group of paths to a route relay corresponding to said group of indirect paths prior to the functioning of said sender to control said switching mechanism.

In a telephone exchange system, a calling office, called oiiices, an intermediate oilioe, switching mechanism located in said calling office, a group of direct paths extending from said switching mechanism to each of said called offices, a group of indirect paths extending from said switching mechanism through said intermediate office to each called o'fiice, a register sender for recording the ofiice code designations of Wanted lines and for controlling said switching mechanism to select a. path to the called ofiice in which a wanted line terminates, a decoder associable with said sender having route relays corresponding to all groups of paths extending from said switching mechanism, operating circuits for said route relays controlled'from said sender in accordance with the office code designation registered therein, and reroute relays in said decoder corresponding to all groups of paths extending from said switching mechanism, each of said reroute relays being operated over a chain circuit closed when all paths ofits corresponding group of paths are busy to transfer the circuit normally effective for operating the route relay corresponding to that group of'paths to a route relay corresponding to said group of indirect paths, prior to the functioning of said sender to control said switching mechanism.

4. In a telephone exchange system, a calling oifice, called oiiices, an intermediate o-flice, switching mechanismlocated in's'aid calling office, a group of direct pathsextending from said switching mechanism to each of said called onices, a

group of indirect paths extending from said switching mechanism through said intermediate oiiice to each called office, a register sender for recording the office code designations of wanted lines and for controlling said switching mechanism to select a path to the called office in which a wanted line terminates, a decoder associable with saidsenderhaving route relays corresponding to all groups ofpaths extending from said switching mechanism, operating circuits for said route relays controlled following the association of said sender with said'decoder in accordance with the office designations registered in said sender, and reroute relays in said decoder corresponding to all groups of paths extending from said switching mechanism, said reroute relays bein operable when all paths of their corresponding groups of paths are busy to transfer the circuits normally effective for operating the route relays corresponding to busy groups of paths to a route relay corresponding to said groups of indirect paths. I

5. In a telephone exchange system, a calling oilioe, called officesan intermediate oiiice, switching mechanism located in said calling office, a group of direct paths extending from said switching mechanism to each of said called ofiices, a group of indirect paths extending from said switching mechanism through said intermediate oflice to each called ofiice, a register sender for recording the oiiice code designations of wanted lines and for controlling said switching mechanism to select a path to the called office in which a wanted line terminates, a decoder associable with said sender having route relays corresponding to all groups of paths extending from said switching mechanism, operating circuits for said route relays controlled following the association of said sender with said decoder in accordance with the oflice code designation registered in said sender, reroute relays in said decoder corresponding to all groups of paths extending from said switching mechanism, saidreroute relays being operable prior to the association of said decoder with said sender over circuits closed when all paths of their corresponding groups of paths are busy to transfer the circuits normally effective for operating the route relays corresponding to busy groups of paths to a route relay corresponding to said group of indirect paths, and means operable upon the association of said decoder with said sender to lock all operated reroute relays and to open the operating circuits of all of said reroute relays.

WARREN W. CARPENTER. 

